Magnesia-containing refractory products and methods of making same

ABSTRACT

A refractory batch mix in which the refractory grain consists essentially of an intimate mixture of (1) selectively calcined dolomite in which the calcium exists substantially as calcium carbonate and the magnesium exists substantially as magnesium oxide, and (2) at least one magnesia-containing grain selected from the group consisting of periclase and dead-burned dolomite.

ited States Patent Leonard John Minnick Cheltenham, Pa. 790,425

Jan. 10, 1969 Nov. 2, 1971 G. & W. 11. Comm, lnc. Plymouth Meeting, Pa.

Inventor App]. No. Filed Patented Assignee MAGNESlA-CONTAINING REFRACTOIiY PRODUCTS AND METHODS OF MAKING SAME 20 Claims, No Drawings US. Cl 106/58,

106/63 Int. Cl C04b 35/06 Field of Search 106/58, 61, 63

Primary Examiner-James E. Poer Anorney- Howson and Howson ABSTRACT: A refractory batch mix in which the refractory grain consists essentially of an intimate mixture of (1) selectively calcined dolomite in which the calcium exists substantially as calcium carbonate and the magnesium exists substantially as magnesium oxide, and (2) at least one magnesia-containing grain selected from the group consisting of periclase and dead-bumed dolomite.

MAGNESlA-CONTAINING REFRACTORY PRODUCTS AND METHODS OF MAKING SAME BACKGROUND OF THE INVENTION .this has'been prepared by calcining magnesite to a deadburned condition or by calcining magnesium hydroxide obtained, for example, from the sea water process. Such compositions have been used in.unshaped form, as inmortars, tamping or ramming'mixes for filling, patching,and the-like; or in the form of shaped bodies, e.g. brick. The brick may be fired or unfired, and may .ormay not be tar bonded or tar impregnated. The particle size of the grain is important andis normally provided by crushing, screening and blending'in a manner adapted to produce a graded materialranging in size and from 4 mesh on down.

The use of dead-burned dolomite has involved several problems. 'In the first place, the preparation of the deadburned dolomite grain involves costly processing steps because of the high temperatures required. in the second place, but of major importance, dead-burned dolomite is unstable on standing under normal atmospheric conditions, as in stockpiles. This involves hydration of the calcium oxide which results in degradation of original particles into small particles consisting of calcium hydroxide and magnesium oxide. Thus,

on standing, the grain size distribution continues to change and the structural properties of the grain are affected deleteriously. Moreover, calcium hydroxide has a lower density than calcium oxide and decomposes at high temperatures, such as in the furnace or during burning of the brick, forming pores and inducing shrinkage. Thus, depending upon the lengthof time of storage; the atmospheric conditions, principally humidity; the size of the stock pile (hydration occurs from the outside of a stockpile inwardly,) and thesize of the particles (hydration occurs from the outside of a particle inwardly), there may be wide variations in the nature of the material in any given stock pile and from brick to brick and from batch to batch in the products made therefrom.

Attempts to overcome this difficulty have involved the installation of expensive air conditioning equipment and storage buildings.

It is the principal object of the present invention to provide a novel magnesia-containing refractory material.

It is another object of the present invention to provide a novel magnesia-containing refractory material in which the foregoing difficulties or problems can be reduced or largely eliminated.

It is another object of the present invention to provide a magnesia-containing refractory composition in which one of the magnesia-containing refractory grains is less expensive to prepare than dead-burned dolomite.

It is a further object 'of the present invention to provide a novel magnesia-containing refractory composition in which one of the magnesia-containing refractory grains is stable on storage even under widely varying atmospheric conditions.

These and other objects, including the provision of methods for making novel magnesia-containing refractory composi: tions, will become apparent from a consideration of the following specification and claims.

SUMMARY OF THE INVENTION The magnesia-containing refractory composition of the present invention is one in which the refractory grain consists essentially of an intimate mixture of (I) selectively calcined dolomite in which the calcium exists substantially as calcium carbonate and the magnesium exists substantially as magnesium oxide, and (2) atleast one magnesia-containinggrain selected-from the group consisting of periclase and deadburned dolomite, the selectively calcined dolomite 'being present in-an amount between about l and about80 percent, by weight, based on the total weight of said refractory grain, substantially all of said'refractory grain being -4 mesh and at least about 30 percent of said selectively calcined dolomite being 30 50 mesh.

It has been found that selectively calcined dolomite can be used in conjunction with periclase and/or dead'bu'rned dolomite to prepare highly valuable basic refractory compositions. The'selectively calcined dolomite isless expensive to prepare than is dead-burned dolomite since it requires much lower calcining conditions. Of importance is the fact that the selectively-calcined dolomite is very stable upon storage'for extended periods ofitime under widely varying atmospheric conditions in that it will not hydrate unde'r' such conditions.

Hence, tothe-extent that it replaces dead-bum'ed dolomite or periclase in refractory compositions, the cost of 'the final refractory product is reducedyand to the extentit replaces dead-burned dolomite,'difficulties due to nonuniforrnity iii the dead-burned'dolomite'grain (through hydration and degradation on storage) are reduced or eliminated. Selectively calcined 'dolomite'is known and is prepared by heating dolomitic limestone at a moderately elevated 'temperature sufficient to convert substantially all of the magnesium carbonate portion to magnesium oxide'but insufficient to convert any substantial amount of the calcium "carbonate to calcium oxide. 'Dolomitic limestone contains calcium carbonate and magnesium carbonate and in an approximately l:l molar ratio, the proportion of each varying, depending upon the source, from about 40 to about 60 percent on a molarbasis. Preferably,-the dolomite'has a purity of at least about 95 percent;ithat isto say, will contain a total of at least about 95 percent CaO-l-MgO on a fully calcined basis. As stated, the selectively calcined dolomite is prepared by calcining dolomitic limestone at a moderately'elevated temperature. Magnesium carbonate decomposes to magnesium oxide at about 1,300 E, and if long calcining times are" available, a temperature at or slightly above this may be used. However, the faster the calcining operation and thelarger the pieces of dolomitic limestone, the higher thetemperature conditions employed. Thus, in some cases, temperatures as high as about l,700 F, may be reached in the limestone. These temperatures, however, are much lower than those required forsubstantially complete calcination of the dolomitic limestone to calcium oxide and magnesium oxide. I

As stated, the other principal component of the refractory composition of the present invention'will be periclase or deadburned dolomite or a mixture of these. Periclase, as is well known, is essentially magnesium oxide as produced by deadbuming natural magnesite, magnesium carbonate or magnesium hydroxide, such as the products obtained by the sea water process. Dead-burned dolomite is also well known 'and is prepared by calcining dolomitic limestone at a temperature well above that sufficient to convert both the calcium c'arbonate and the magnesium carbonate to their respective oxides. y

In the refractory compositions of the present invention, the selectively calcined dolomite will make up at least l0 percent, by weight, based on the total weightof the refractory grain. A proportion as high as about percent thereof may be employed, although,in most cases, the amount of the selectively calcined dolomite will not exceed about 60 percent. In accordance with preferred practice, the selectively calcined dolomite will make up between about 30 and about 50 percent, by weight, based on the total weight of the refractory grain.

In the refractory compositions of the present invention, substantially all of the grain will be 4 mesh (Tyler). ln 'accordance with conventional refractory practice, there will be a size gradation. Thus, it is preferred that from about 30 to about 70 percent, by weight. of the refractory grain be -4+50 mesh and the balance (from about 70 to about 30 percent) be 50 mesh. It has been found that at least about 30 percent of the selectively calcined dolomite should have a particle size greater than 50 mesh, and, in accordance with preferred prac- 4 siz e of the fired product is uniform and reproducible from batch to batch.

The invention will be more readily understood from a consideration of the following specific examples which are given tice, at least about 50 percent of the selectively calcined '5 for the purpose of illustration only and are not to be condolomite will have a particle size greater than 50 mesh. sidered as limiting the scope of the invention: EXAMPLES The composition of the present invention may be used in es- 1-8 sentially unshaped form. For example, it may be tempered In these examples periclase and selectively calcined with water to form a mortar or rammed or tamped into place dolomite are blended in various proportions as set forth in to form a monolithic structure. The preparation of unshaped table I. The periclase contains 95-96 percent MgO, and the mixes from magnesia-containing refractory grain is well selectively calcined dolomite has a mol ratio of CaCO;,: MgO known and the general procedures applicable there are of approximately 1:1 and contains 95-96 percent CaC0,+M- likewise applicable to the present invention. g0.

On the other hand, the composition may be prepared and In table I are set forth the proportions (in weight percent used in the form of a shaped body, such as a brick. The brick based on the total weight of periclase and selectively calcined may be unburned and chemically bonded or it may be burned dolomite) of each material in the given particle size range (fired) to develop a ceramic bond among the refractory grain (mesh, Tyler):

. TABLE I Periclase Selectively calcined dolomite 4 8 l6 50 100 -200 325 4 8 16 30 50 100 -200 325 Example +8 +16 +30 +50 +100 +200 +325 +8 +16 +30 +50 +100 +200 +325 P/D 20.0 Weight ratio of periclase to selectively calcined dolomite.

particles. The preparation of unburned, chemically bonded Each of the foregoing mixes is dry blended after which a brick and also of burned brick, from magnesia-containing temporary binder (4 percent molasses and 4 percent water, by refractory grain, is well known and the general procedures apweight, and based on 100 parts of the dry mix) is added and plicable there are likewise applicate to the present invention. mixed therewith. Each damp mix, in an amount of 350 g. is For example, in preparing burned brick from the composition placed in a 4%X2 54-inch brick mold and pressed at 10,000 of the present invention, the composition is pressed, either in p.s.i. for 10 minutes. After removal from the mold, each dry form or after tempering with water and a temporary specimen is dried at 100 C. for 16 hours and then fired at binder, into brick fonn and the brick shape is fired at a temf r 5 h perature ranging from about 2,600 to about 3,500" F. de- 40 Data obtained are setfortl in the follo vlng table ll: pending upon the particular kiln employed and hence the time TABLE II available. During such firing calcium carbonate in the selectively calcined dolomite decomposes to calcium oxide. Example 1 2 3 4 5 6 7 8 The composition of the present invention is particularly ap- Unfired formed brick i q I 84 86 88 90 plicable for the preparation of well-known tar-containing brick. In this case, either one of two generally well-known firlrlgmqrcent -2 23 3 3 2 g procedures may be followed: l) tar may be mixed with the Fired density 16 composition following which the mixture is pressed into brick l "T W r 1 form; the resulting brick "WP? heated to drive volatiies; cri l t ini fv l iil e t h os 32222531: 7 and zhow omz 5:51;; (2) a i t may be "I prepared followmg much that might, however, not be objectionable in some applicathe brick IS impregnated with molten tar to prevent submm sequent hydrauon of calclum, In the lan er In similar fashion,apart or all of the periclase in the foregovacuum-pressure sequence durmg which the brick s placed in ins mixed may be replaced by dcadbumed dolomite.

a chamber wh|ch lS evacuated, molten tar IS admitted to the chamber and the vacuum released and pressure applied to EXAMPLES force the molten well into the brick, as well as to coat the sur- The fi d brick f examples 2'3, 4 and 5 are impregnated face is usually p y The m as used in this with pitch by placing the brick in a sealed chamber, evacuattext is used in the generic sense to include pitches, resins and ing the chamber and then admitting molten pitch having a like P1110360!e materials which decompose t0 carbon melting point of about 160 F., under pressure until the brick upon heating. The amount of "tar generally ranges up to are impregnated with 10-15 percent, by weight, ofthe pitch. about 15 percent by weight, based on the weight of the refrac- EXAMPLE 13 tory grain, depending upon the particular material used.

The compositions of the present inventions may be used as in this example are mixed 40 parts, by weight, of the seleclinings, patching material, and the like, in refractory-lined aptively calcined dolomite used in the preceding examples, (but paratus where high temperatures are encountered such as rehalf is 4+50 mesh and half is 50+100 mesh, Tyler); and 60 torts, furnaces, kilns, and the like. parts of the periclase as used in the preceding examples, but

Since the compositions of the present invention contain calhalf of which is l6+l 00 mesh and the other half l00 mesh. cium carbonate which will decompose at high temperatures, Specimens are pressed, dried and fired as in examples 1-8 to some shrinkage will occur at high temperatures depending provide excellent brick exhibiting a shrinkage on firing of upon the relative proportion of the selectively calcined 0.4-6 percent (linear) and 1.3-1.9 percent (volumetric). dolomite in the product. However, in the proportions called Modification is possible in the selection of selectively calfor herein, there is no deleterious warping or cracking of the cined dolomite, periclase and dead-bumed dolomite as well as product under such temperature conditions. In the preparain the selection of binders, if used, tar," if used, and proportion of fired brick, any shrinkage involved can be compentions and processing techniques without departing from the sated for by employing an oversized mold so that the ultimate 7 scope of the present invention.

What is claimed is:

1. A refractory batch mix of refractory grain in which the refractory grain consists essentially of an intimate mixture of (1) selectively calcined dolomite in which the calcium of said dolomite exists substantially as calcium carbonate and the magnesium of said dolomite exists substantially as magnesium oxide, and (2) at least one magnesia-containing grain selected from the group consisting of periclase and dead-bumed dolomite, said selectively calcined dolomite being present in an amount between about and about 80 percent, by weight, based on the total weight of said refractory grain, substantially all of said refractory grain being -4 mesh and at least about 30 per cent of said selectively calcined dolomite being +50 mesh.

2. The refractory batch mix of claim 1 wherein said selectively calcined dolomite is present in amount less than 60 percent.

3. The refractory batch mix of claim 2 wherein said selectively calcined dolomite is present in an amount between about 30 and about 50 percent.

4. The refractory batch mix of claim 1 wherein at least about 50 percent of said selectively calcined dolomite is +50 mesh. 50

5. The refractory batch mix of claim 2 wherein at least about 50percent of said selectively calcined dolomite is +50 mesh.

6. The refractory batch mix of claim 3 wherein at least about 50 percent of said selectively calcined dolomite is +50 mesh.

7. The refractory batch mix of claim 1 wherein from about 30 to about 70 percent of said refractory grain is 4 +50 mesh and the remainder is ---50 mesh.

8. The refractory batch mix of claim 2 wherein from about 30 to about 70 percent of said refractory grain is 4+50 mesh and the remainder is -50 mesh.

9. The refractory batch mix of claim 3 wherein from about 30 to about 70 percent of said refractory grain is 4 +50 mesh and the remainder is -50 mesh.

10. The refractory batch mix of claim 4 wherein from about 30 to about 70 percent of said refractory grain is 4+50 mesh and the remainder is -50 mesh.

11. The'refractory batch mix of claim 5 wherein from about 30 to about 70 percent of said refractory grain is 4+50 mesh and the remainder is -50 mesh.

12. The refractory batch mix of claim 6 wherein from about 30 to about 70 percent of said refractory grain is 4+50 mesh and the remainder is -50 mesh.

13. The method of making a magnesia-containing refractory brick which comprises pressing. into brick form refractory batch mix of refractory grain in which the refractory grain consists essentially of an intimate mixture of (l) selectively calcined dolomite in which the calcium of said dolomite exists substantially as calcium carbonate and the magnesium of said dolomite exists substantially as magnesium oxide, and (2) at least one magnesia-containing grain selected from the group consisting of periclase and dead-burned dolomite, said selectively calcined dolomite being present in an amount between about 10 and about percent, by weight, based on the total weight of said refractory grain, substantially all of said refractory grain being -4 mesh and at least about 30 percent of said selectively calcined dolomite being +50 mesh.

14. The method of making a magnesia-containing refractory brick which comprises pressing into brick form a refractory batch mix of refractory grain in which the refractory grain consists essentially of an intimate mixture of (l) selectively calcined dolomite in which the calcium of said dolomite exists substantially as calcium carbonate and the magnesium of said dolomite exists substantially as magnesium oxide, and (2) at least one magnesia-containing grain selected from the group consisting of periclase and dead-burned dolomite, said selectively calcined dolomite being present in an amount between about 30 and about 50 percent, by weight, based on the total weight of said refractory grain, from about 30 to about 70 percent of said refractory grain being -4+50 mesh and the remainder +50 mesh and at least about 50 percent of said selectively calcined dolomite is +50 mesh.

15. The method of claim 13 wherein tar is mixed with said refractory grain before pressing.

16. The method of claim 14 wherein tar is mixed with said refractory grain before pressing.

17. The method of claim 13 wherein said brick form is fired.

18. The method of claim 14 wherein said brick form is fired.

19. The method of claim 17 wherein the resulting fired brick is impregnated with molten tar.

20. The method of claim 18 wherein the resulting fired brick is impregnated with molten tar.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,617,518 Dated January 26, 1972 Inventor(s) Leonard John Minnick It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

2, 1. 8, "30" should read Col. 4, l. 53, "mixed" should read mixes Col. l. 70, "0.4-6" should read (L -0.6

Col. 6, l. 31, "+50" should read -5O Signed and sealed this 26th day of December 1972.

(SEAL) Attest:

EDWARD BLFLETCHER IR. ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents U 5 GOVERNMENT PRINYING OVHLI I969 0]56314 

2. The refractory batch mix of claim 1 wherein said selectively calcined dolomite is present in amount less than 60 percent.
 3. The refractory batch mix of claim 2 wherein said selectively calcined dolomite is present in an amount between about 30 and about 50 percent.
 4. The refractory batch mix of claim 1 wherein at least about 50 percent of said selectively calcined dolomite is +50 mesh. 50
 5. The refractory batch mix of claim 2 wherein at least about 50percent of said selectively calcined dolomite is +50 mesh.
 6. The refractory batch mix of claim 3 wherein at least about 50 percent of said selectively calcined dolomite is +50 mesh.
 7. The refractory batch mix of claim 1 wherein from about 30 to about 70 percent of said refractory grain is -4 +50 mesh and the remainder is -50 mesh.
 8. The refractory batch mix of claim 2 wherein from about 30 to about 70 percent of said refractory grain is -4+50 mesh and the remainder is -50 mesh.
 9. The refractory batch mix of claim 3 wherein from about 30 to about 70 percent of said refractory grain is -4 +50 mesh and the remainder is -50 mesh.
 10. The refractory batch mix of claim 4 wherein from about 30 to about 70 percent of said refractory grain is -4+50 mesh and the remainder is -50 mesh.
 11. The refractory batch mix of claim 5 wherein from about 30 to about 70 percent of said refractory grain is -4+50 mesh and the remainder is -50 mesh.
 12. The refractory batch mix of claim 6 wherein from about 30 to about 70 percent of said refractory grain is -4+50 mesh and the remainder is -50 mesh.
 13. The method of making a magnesia-containing refractory brick which comprises pressing into brick form refractory batch mix of refractory grain in which the refractory grain consists essentially of an intimate mixture of (1) selectively calcined dolomite in which the calcium of said dolomite exists substantially as calcium carbonate and the magnesium of said dolomite exists substantially as magnesium oxide, and (2) at least one magnesia-containing grain selected from the group consisting of periclase and dead-burned dolomite, said selectively calcined dolomite being present in an amount between about 10 and about 80 percent, by weight, based on the total weight of said refractory grain, substantially all of said refractory grain being -4 mesh and at least about 30 percent of said selectively calcined dolomite being +50 mesh.
 14. The method of making a magnesia-containing refractory brick which comprises pressing into brick form a refractory batch mix of refractory grain in which the refractory grain consists essentially of an intimate mixture of (1) selectively calcined dolomite in which the calcium of said dolomite exists substantially as calcium carbonate and the magnesium of said dolomite exists substantially as magnesium oxide, and (2) at least one magnesia-containing grain selected from the group consisting of periclase and dead-burned dolomite, said selectively calcined dolomite being present in an amount between about 30 and about 50 percent, by weight, based on the total weight of said refractory grain, from about 30 to about 70 percent of said refractory grain being -4+50 mesh and the remainder +50 mesh and at least about 50 percent of said selectively calcined dolomite is +50 mesh.
 15. The method of claim 13 wherein tar is mixed with said refractory grain before pressing.
 16. The method of claim 14 wherein tar is mixed with said refractory grain before pressing.
 17. The method of claim 13 wherein said brick form is fired.
 18. The method of claim 14 wherein said brick form is fired.
 19. The method of claim 17 wherein the resulting fired brick is impregnated with molten tar.
 20. The method of claim 18 wherein the resulting fired brick is impregnated with molten tar. 